Polyurethane and polyisocyanurate foam insulation boards are commonly employed in the construction industry. These insulation boards are generally cellular in nature and typically include an insulating compound trapped within the cells of the foam. For example, it is common to produce insulation boards by employing hydrofluorocarbons, hydrochlorofluorocarbons and hydrocarbons as a blowing agent, which thereby entraps these compounds within the cell network for purposes of improving the insulating ability of the foam.
In addition to the insulating ability of the insulation boards, the physical characteristics of the board are likewise important to the overall performance of the board. For example, dimensional stability is important because insulation boards are exposed to a full range of weather. Where insulation boards are employed to insulate flat or low-slope roofs, shrinkage of these insulation boards from cold temperatures can cause a loss of insulating efficiency. As a result, it is common in the industry to test insulation boards for cold-age dimensional stability (ASTM D2126). Alternatively, the dimensional stability of insulation boards, primarily the 8 foot edges of a standard 8″×4″ board, c an be determined by analyzing the perpendicular compressive strength in the cross machine direction. The higher the perpendicular compressive strength, the better the cold age dimensional stability.
The dimensional stability of insulation boards is believed to be impacted, especially near the edges of the board, by the degree of polyurethane crosslinking (isocyanurate formation). Incomplete crosslinking tends to be a problem near the edges of the board because less heat is present at the edges following manufacture of the boards. In other words, the boards are typically stacked or bundled following manufacture and the heat that is generated and trapped within the boards tends to drive crosslinking; the exposed surface area around the edges of the stacks or bundles allows the edges to cool more rapidly which results in decreased crosslinking.
Also, the use of certain blowing agents tends to promote dimensional instability. Namely, it is believed that certain hydrochlorofluorocarbons are rather soluble in the polymeric network of the board. As a result, the polymer network tends to plasticize the polymer network, which results in reduced network integrity.
Because insulation boards made of polyurethane or polyisocyanurate foams remain important articles for the construction industry, there is a need to improve the physical characteristics of the boards, such as cold age dimensional stability.